WASHINGTON -LRB- CNN -RRB- -- The FBI and the Department of Homeland Security issued a bulletin Thursday citing an alleged claim of responsibility by al Qaeda for former Pakistani Prime Minister Benazir Bhutto 's assassination , a DHS official told CNN .

An Italian news agency says al Qaeda No. 2 Ayman al-Zawahiri began planning Bhutto 's killing in October .

But such a claim has not appeared on radical Islamist Web sites that regularly post such messages from al Qaeda and other militant groups .

The source of the claim was apparently Italian news agency , Adnkronos International -LRB- AKI -RRB- , which said that al Qaeda Afghanistan commander and spokesman Mustafa Abu Al-Yazid had telephoned the agency to make the claim .

`` We terminated the most precious American asset which vowed to defeat -LSB- the -RSB- mujahadeen , '' AKI quoted Al-Yazid as saying .

According to AKI , al Qaeda No. 2 Ayman al-Zawahiri set the wheels in motion for the assassination in October .

One Islamist Web site repeated the claim , but that Web site is not considered a reliable source for Islamist messages by experts in the field .

The DHS official said the claim was `` an unconfirmed open source claim of responsibility '' and the bulletin was sent out at about 6 p.m. to state and local law enforcement agencies .

The official characterized the bulletin as `` information sharing . ''

Ross Feinstein , spokesman for Director of National Intelligence Mike McConnell , said the U.S. intelligence community is monitoring the situation and trying to figure out who is responsible for the assassination .

`` We are not in a position to confirm who may be responsible , '' Feinstein said .

Feinstein said that the intelligence community `` obviously analyze -LRB- s -RRB- open source intelligence , '' but he would not say whether the community believes the claim has any validity .

For now , he said , there is `` no conclusion '' as to who may be responsible .

Earlier , DHS spokesman Russ Knocke said Bhutto 's assassination had not prompted `` any adjustments to our security posture . ''

`` Of course , we continue to closely monitor events as they unfold overseas , '' he said . E-mail to a friend

CNN 's Jeanne Meserve contributed to this report .

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FBI , Department of Homeland Security issue bulletin Thursday

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Bulletin says two al Qaeda associates made claim to news agency

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`` We terminated the most precious American asset , '' associate says

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DHS official says the claim has not been confirmed